7.2-inch H.E. "Mouse Trap" and 2.5-inch Practice

Over-all length, inches

Head length, inches

Head weight, pounds

Filler weight (TNT), pounds

Wall thickness, inch

Motor length, inches

Motor diameter, inches

Motor weight, pounds

Tail width, inches

Total weight, pounds

65

General: This rocket was designed for use by patrol vessel against submarines. The most common installation consists of two four-rail Launchers Mk 20, with a fixed eleva-tion of 48°, mounted on the fore deck with firing controlled from the bridge.

Complete Rounds

Assembly No.

Head

Filling

Grain

Fuze

7.2" H.E. 208

7.2" Mk 4

TNT

Mk 3

Mk 131 - Mk 156

(Obsolete)

7.2" H.E. 211

7.2" Mk 5

TPX

Mk 3

Mk 131 - Mk 156

7.2" H.E. 212

7.2" Mk 5

TPX

Mk 3

Mk 140 - Mk 156

7.2" H.E. 213

7.2" Mk 5

TNT

Mk 10

Mk 131 - Mk 156

7.2" H.E. 216

7.2" Mk 5

TNT

Mk 10

Mk 140 - Mk 156

7.2" H.E. 217

7.2" Mk 4

TNT

Mk 3

Mk 140 - Mk 156

In addition to the service rounds, there are the Mks 106 and 109 filled with plaster for target practice, and the Mks 206 and 209 filled with plaster for drill.

Head: The projectile consists of a flat-nosed head with a conical tail fairing and pa-rallel sides. The adapter and fuze thread into the nose, and the motor unit threads into the base.

Motor: The Motor Unit Mk 3 contains a long single pellet of smokeless powder which, when ignited by a black-powder primer fired by an electric squib, burns at a pressure of 1,000 to 2,500 pounds per square inch. The gases are forced out aft through the nozzle in the rear end of the motor tube. The burning continues for 0.2 to 0.7 second, during which time the missile travels about 30 feet. At this point, propulsion ceases and the projectile is free in flight. This projector charge is intended for use on the 7.2-inch Roc-ket Launchers Mk 20, Mk 21, or Mk 22.

Tail: A steel tube attached to the head by a threaded joint has fins with two circular drums attached to the after end. The vanes have a 10-degree twist to give a slow rota-tion and prevent ruddering. The two vane-support drums also act as contact rings, the wiring from the electric squb passing from the primer aft to the two rings which serve as firing contacts.

Remarks: When Torpex is used, the weight is increased by approximately 2.5 pounds.

The 2.5-inch sub-caliber rocket, consisting of the 1.25-inch Motor Mk 1 and 2.5-inch Head Mk 1, is a miniature of the regular rocket and is used in practice. The motor con-tains a single tubular powder grain, an igniter, and lead wires. The tail fins, supported by a shroud, are offset five degrees to impart some rotation to the round, to improve under-water travel. The Head Mk 1 has a cavity for a shot-gun shell; the Head Mod 2 Mk 1 is solid.

The Fuzes Mk 131 and Mk 140 are replaced by the Mk 156 in the service rounds.